The long-term goal of this research program is to obtain fundamental new information on the mechanism of steroid hormone action in the mammalian uterus. The previous results from this laboratory have established the utility of the decidualized hamster uterus for experimental studies of receptor regulation and specific protein synthesis in different uterine cell types, i.e., the decidual cell and uterine smooth muscle cell. The current application proposes to continue this research program for a five-year period with the following specific aims: 1. to determine the relative importance of estrogen (E)+ progesterone (P) in the regulation of steroid receptors in the deciduoma and myometrium. What is the critical E/P ratio for determining up and down regulation of estrogen and progesterone receptors in different uterine cell types? 2. to identify cell-specific and hormone-specific proteins in decidual cells. 3. to develop specific antibodies to decidual marker proteins. 4. to study the specific effects of steroid hormones (E and P), cyclic nucleotides (cAMP, cGMP) and prostaglandins on steroid receptors and macromolecular synthesis in decidual cells. These studies will provide information relevant to the treatment of hormone-dependent tumors and the development of new contraceptive techniques.